The present invention relates a refrigeration system incorporating a scroll type compressor equipped with a gas injection mechanism.
Generally, a scroll type compressor is constituted by an orbiting scroll member having an end plate and a wrap formed along an involute curve or a curve approximately an involute curve so as to protrude upright from one side of the end plate, and a fixed scroll member having an end plate provided with a central discharge port and a peripheral suction port and a wrap similar to that of the orbiting scroll member and protruding upright from the end plate. The orbiting scroll member and the fixed scroll member are assembled together such that their wraps mate with each other, and are housed by a common housing which is provided with a suction pipe and a discharge pipe.
An Oldham's ring is disposed between the orbiting scroll member and the frame of the compressor or between the orbiting scroll member and the fixed scroll member, so as to prevent the orbiting scroll member from rotating around its own axis. A crank shaft engaging with the orbiting scroll member causes an orbiting motion of the orbiting scroll member without permitting the latter to rotate around its own axis so that a gas confined in the closed chmabers defined by the scroll members is progressively compressed and discharged from the discharge port. An example of this scroll-type compressor is disclosed in, for example, U.S. Pat. No. 3,884,599.
The flow rate of the gas compressed by this compressor is determined by the specific volume of the gas sucked into the suction chamber formed between two scroll members and by the maximum confinement volume which is created when the suction chamber is changed into a compression chamber as a result of the orbiting motion of the orbiting scroll member. Since this maximum confinement volume is fixed, the flow rate is maintained constant provided that the specific volume of the gas is unchanged.
As to the air conditioning throughout a year, the heating load demanded in winter season is greater than the cooling load in the summer season. In this connection, it is to be noted that the ratio between the cooling capacity and heating capacity is almost one, i.e. the cooling capacity and the heating capacity are almost equal, in ordinary heat-pump type air conditioner incorporating a refrigeration system. This means that the shortage of heating capacity in winter season is inevitable. To make up for the shortage of the heating capacity, it is a common measure to provide an additional heat source such as an electric heater to assist the air conditioner in effecting the heating in the winter season. However, since the increase in the heating capacity is equal to the increase in the input power, the energy efficiency ratio is much smaller than that attained when no electric heater is used.
A system called "gas injection system" is known for increasing the capacity of the air conditioner without using any additional heat source such as electric heater. The gas injection system incorporates a rotary compressor, a screw compressor and so forth, and has the following features.
A first expansion valve is disposed at the downstream side of the condenser of a refrigeration system, and a gas-liquid separator is connected to the downstream side of the first expansion valve. The gas-liquid separator has a gas outlet and a liquid outlet. A second expansion valve is connected to the downstream side of the liquid outlet of the gas-liquid separator, and the outlet side of the second expansion valve is connected to an evaporator. On the other hand, the gas outlet is connected to a gas injection port which opens to a compression chamber on its way of compression. Consequently, the pressure in the gas-liquid separator is maintained at an intermediate level between the suction pressure and the discharge pressure.
In this type of gas injection system, there are provided two refrigerant circuits: namely, a circuit constituted by a loop starting from the compressor and ending in the same through the condenser, first pressure reducer, gas-liquid separator, second pressure reducer, and the evaporator; and a circuit constituted by a loop which is common to the first circuit from the compressor down to the gas-liquid separator but shunts from the first circuit at the separator and leads to the compressor.
In the gas injection system, the rate of heat extracted is increased in the evaporator because of a large difference in enthalpy of the refrigerant between the inlet and outlet of the evaporator, while, in the condenser, the heat discharge is increased because of an increase in the flow rate of the refrigerant. Thus, the gas injection system conveniently increases both of the heating capacity and cooling capacity.
According to the gas injection system, the increase of the compression work due to an increase of the flow rate of refrigerant takes place only in a part of the whole compression work, i.e. from a point intermediate of the compression to the end of the discharge. This increase is much smaller than the increase of the compression work which would be incurred in a single-stage compressor when the injection of the additional refrigerant is made from the beginning of the compression. This means that the gas injection system advantageously offers an increase in the energy efficiency ratio. Unlike the case of the electric heater, the increase in the capacity offered by the gas injection is achieveable not only in the heating mode but also in the cooling mode of the operation. It is, therefore, possible to make the gas injection, for a while after a starting of the cooling operation, accelerate the cooling in the period immediately after the start up of the air conditioner.
When the gas injection system is applied to a compressor which completes one cycle by one rotation, e.g. a rotary compressor or a screw compressor, the rate of increase of the pressure in the compression chamber is so large that the gas injection is allowed only for a limited period. Therefore, in order to effect the gas injection at a large rate it is necessary to preserve a large area of the injection port. However, the increase area of the injection port is accompanied by an increase in the gap volume of the compression chamber which, in turn, increases the internal leak of the gas disadvantageously resulting in an increased loss of power.
Furthermore, in the rotary compressor, the injection port opens substantially over the entire area of the compression stroke so that it is necessary to employ a suitable means for preventing the reversing of the refrigerant from the compression chamber or for limiting the period of the injection in such a manner as to prevent the injection in the period in which the internal pressure of the compression chamber exceeds the injection pressure.
There have been no proposals as to the adoption of the gas injection system in a refrigeration system having a scroll type compressor, although in Japanese Utility Model Laid-Open No. 85807/1981 proposes a liquid injection system resembling a gas injection system to a refrigeration system having a scroll type compressor. However, this liquid injection system is intended for cooling the compressor by introducing liquid refrigerant into the compression chamber under compression, to thereby suppress a temperature rise in the winding of motor or lubricating oil to prevent degradation and burning of the bearing.
While the discharge rate is increased as a result of the proposed liquid injection, the total heating capacity is unaltered because the enthalpy of the refrigerant is lowered at the condenser inlet. The evaporator side is materially identical to that in the ordinary refrigerant circuit and the refrigeration power is materially equivalent to that of the ordinary refrigeration system. Moreover, the liquid injection system imposes a problem that the energy efficiency ratio is reduced due to an increase of input to the compressor.
Japanese Patent Laid-Open No. 81513/1979 discloses a scroll type compressor in which a part of the gas discharged from the discharge port of the compressor and is cooled and then sent to a pressure reducer which reduces the pressure of the cooled gas to an intermediate pressure. The gas of the intermediate pressure is then introduced into the housing of the compressor to impart an axial pressing force to the orbiting scroll member. In addition, an injection port communicating with the housing is formed in the fixed scroll member or the orbiting scroll member and the gas is injected through this injection port into the closed space defined between the wraps of the orbiting scroll member and fixed scroll member to thereby cool the bearing and the back side of the orbiting scroll member, as well as the driving motor. However, the injection of the gas in this compressor is not intended to increase the heating or cooling capacity.